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Rinodina calcigena (Th. Fr.) Lynge
Family: Physciaceae
Rinodina calcigena image
Thompson, J., 1997. American Arctic Lichens: The Microlichens.
Thallus brown or gray where eroded, scant, only around base of apothecia or of scattered granules, 0.3 mm diameter, rarely thicker, verruciform or areolate, shining or dull. Apothecia 1-3 per areola, at first innate and erumpent, becoming sessile, to 0.9 mm broad; margin either of same color as disk or as thallus; thalloid exciple cellular and with an epicortex; proper exciple 10-20 μm, broadening to 10-50 μm above; disk black, flat becoming convex, sometimes pruinose; hypothecium hyaline, developing a stipe; epihymenium dark brown; hymenium inspersed; paraphyses 2.0-3.5 μm, tips 4-6.5 μm and very dark; asci clavate; spores of bischoffii-type, that is, with outer walls at septum invaginated and darkened, forming a lightly pigmented band around center of spore, a porus also being present, 16-24 x 9.5-13 μm.

This species grows on calcareous rocks. It is known from Scandinavia, Spitzbergen, Novaya Zemlya, Greenland, Alaska, and arctic Canada, south to Colorado. It thus appears to be circumpolar arctic.

The closely related Rinodina castanomela (Nyl.) Arnold, which differs from this only in having a thick, areolate, and marginally lobed thallus, has been reported from Disko Island, Greenland, by Hansen (1984, p. 312).